PDP 11/45 partial success.

[Tom Uban]

Nice detective work Jim. Unless your "spare" UBC is known good and has
the same revision as your defective card, I would suggest replacing the
IC on your card and proceeding with the diagnosis. Otherwise, you may
just replace one set of symptoms with another.

--tom

At 08:42 PM 3/18/2005 +0000, you wrote:

>Hi All,
>
>after a few days frustration, I have got a little further with my 11/45.
>
>The power supplies checked out OK with respect to ripple and output, but a
>couple have them have the odd VERY fast spike on them - is this normal? (I'm
>using a 100MHz 'scope - I suspect they may not be visible on a slower one).
>
>After reducing the machine to its basics, I found I could load an address
>from the front panel, but not write or examine any location successfully.
>The address and data lines became active, but the processor then goes into a
>pause state. I found that the MSYN line was not being asserted, and it
>appears that one ic on the Unibus controller (M8106) is not providing the
>correct ouput - grounding the scope probe will force the line, and the
>processor completes its bus cycle (Yes the inputs to the ic are correct!).
>
>I have found a spare serviceable UBC, so I'll try that when I next get
>chance, and if that fixexs the fault, I'll repair mine.
>
>Jim.
>
>Please see our website the " Vintage Communication Pages" at WWW.G1JBG.CO.UK